In recent years, display apparatuses using an organic electroluminescence (EL) device have attracted great attention as display apparatuses which can be made thinner and more lightweight, as compared to conventional CRTs and LCDs. The organic electroluminescence device is of a self-emitting type, and thus it offers various advantages such as providing high visibility, being free from angle-of-field dependency, allowing use of a film substrate having flexibility, being thinner and more lightweight compared to a liquid crystal display apparatus, and the like. Further, in order to realize a display with higher fineness, development of an active matrix type display apparatus having a switching device, such as a thin film transistor, or the like, together with the organic electroluminescence device has been under progress.
In a conventional display apparatus which uses an organic electroluminescence device, an anode electrode made from a transparent conductive film such as ITO (indium oxide doped with tin) is formed on an insulating substrate made from, for example, a glass substrate. On the anode electrode, an organic electroluminescence layer including a luminescence layer where an electron and a hole are recombined to generate light is formed. On the organic electroluminescence layer, a cathode electrode made from an Al (aluminum) film, an Mg (magnesium)-Ag (silver) alloy film, or the like, is formed. Thus, on the insulating substrate, the organic electroluminescence device having the anode electrode, the organic electroluminescence layer, and the cathode electrode is formed. In addition, in the active matrix type display apparatus, a switching device, such as a thin film transistor, or the like, which controls the driving voltage to be applied to the organic electroluminescence device is formed between the insulating substrate and the organic electroluminescence device. The display apparatus having such a structure is a so-called bottom emission type apparatus, wherein the light generated in the luminescence layer in the organic electroluminescence layer is taken out from the insulating substrate side.
When full colorization is to be realized with the above-mentioned display apparatus, luminescence layers which are different in luminescence wavelength are formed in the pixel regions. For example, a vapor deposition mask in which apertures for the pixel regions are formed is tightly contacted with the substrate, and by displacing the vapor deposition mask in the order of RGB, for example, the luminescence layers for generating the respective RGB colors are formed.
In the bottom emission type display apparatus, the light generated in the organic electroluminescence device is taken out from the insulating substrate side, as described above. Therefore, in the case where a switching device is formed between the insulating substrate and the organic electroluminescence device, there is a problem that the luminescence area in one pixel is substantially reduced due to the existence of the switching device, which makes it impossible to obtain a high luminous efficiency.
Attempts to eliminate this problem of luminous efficiency have been made by adopting the so-called top emission type structure, wherein the light generated in the luminescence layer is taken out from the side opposite to the insulating substrate side on which the switching device is formed, in other words, from the cathode electrode side (see, for example, patent documents 1 and 2).
In the top emission type display apparatus as disclosed in patent document 1, a cathode electrode having light transmittance is used, and as an anode electrode, a Cr (chromium) thin film having light reflectivity is used, whereby the light generated in the luminescence layer is reflected to the cathode electrode side, and from the cathode electrode, the light is taken out. However, since the light reflectance of Cr is not particularly high, the light generated in the luminescence layer cannot be sufficiently reflected to the cathode electrode side.
In addition, in the top emission type display apparatus as disclosed in patent document 2, an electrode layer made from an ITO film is formed directly on a reflection layer made from an Al film. However, the electrical connection between the Al film and the ITO film is not good, and thus it has been difficult to use the reflection layer as the electrode.
Therefore, if a switching device is provided under the reflection layer, establishing a connection between the electrode layer and the switching device has been difficult.
An object of the present invention is to provide an organic electroluminescence device which can realize a high luminous efficiency, and a manufacturing method therefor, as well as a display apparatus having such an organic electroluminescence device.
Patent document 1: Japanese Patent Laid-Open Publication No. 2001-85163
Patent document 2: Japanese Patent Laid-Open Publication No. 11-329753/1999